Polymerization of conjugated diene hydrocarbons



' either would not homogenize in general possess mercaptoe,

Patented July 31, 1945 2,380,426 U POLYMEBIZA'ITON OF CONJUGATED DIENE I nrnnocmnons Silver Lake, om, mm, to

Charles F. Fryiing,

The B. F. Goodrich Company, New York, N. Y., a corporation of New York No Drawing. Application May 31, 1941, Serial No. 396,155

14 Claims. (Cl. 260-845) This invention relates to the polymerization of butadiene hydrocarbons, and particularlyto a method whereby butadiene hydrocarbons may be polymerized in an aqueous emulsion to form products closely resembling natural crude rubber.

The emulsion polymerization of butadiene hydrocarbons either alone or in admixture with other monomers copolymerizable therewith to form compositions of matter more or less resembling rubber is well known. It has been commonly observed, however, that the products of such polymerization often resemble vulcanized rubber rather than natural crude rubber in respect to solubility,

acteristics. Thus it has often been found that the polymers were insoluble in. and, in some cases,

not even swelled by benzene or acetone, and that they were tough, non-plastic materials which on a mill or-which were very-diflicult to mill and to subject to other ordinary processing operations.

I have now discovered a class of materials which-modifies the emulsion polymerization of butadiene hydrocarbons in such a manner that polymers more nearly resembling natural crude rubber may be produced than when the polymerization is carried on in the absence of the materials of this invention. This class of materials, which I have termed "modifiersf? consists of compounds, containing the Z-thiothiazyl group which may be represented by the following structural formula:

not form part of an unsaturated carbocyclic ring,

such as 2-mercapto-4-ethylthiazole, 2-mercapto- 4-phenylthiazole, 2-mercapto-4,5-dimethylthiazole, li-mercapto-i-methoxymethylthiazole, and the corresponding bis-thiazyl-2 mono, di;-, and polysulfldes, the aliphatic bis-thiazyl-2 disulfides producing especia y goo results. Other compounds which may be employed but which do not lie-great activity asthe aliphatic z-mercaptothiazolee include the aromatic thiazoles, by which is meant compounds in which 4 numbered 4 and 5' iorm part otanunsaturatedcarboqdhflhtnifiasflz-mercaptonaphthothiasole. and-the plasticity, and processing chara 3% solution of myristic 85% neutralized with sodium hydroxide, and 0.35

mono-, di-, and polys'ulfldes'. Z-thiazyl sulfides such as 4,5-dimethylthiazyl-2 diethylamino sulfide, benzothiazyl-2 dicyclohexylamino sulfide and other compounds containing the 2-thiothiazyl group may also be employed. While the compounds in which the basicity is increased by the presence of nitrogenous substituents exhibit activity as modifiers, they also retard the polymeriz'ation. The retarding action may in general be counteracted, however, by known methods of accelerating polymerization reactions.

The efiect of compounds containing the 2-thiothiazyl group on emulsion polymerization is shown by the copolymerization at C. of parts by weight of butadiene and45 parts of acrylonitrile in the presence of about 250 partsoi acid which had been part of hydrogen peroxide as an initiator. Although the polymer obtained by coagulating the latex formed by polymerization in the absence of any modifier was in the form of non-plastic, noncoherent crumbs, the polymer obtained when 0.5

aliphatic 2-merpart of 2-mercapto-4-ethy1thiazole were present in the emulsion during the polymerization was a soft, plastic,. coherent synthetic rubber. When the polymer prepared in the absence of the thiazole was vulcanized in a tire tread test recipe, 9. vulcanizate exhibiting a tensile strength of 3400- 3850 lbs./in. and an elongation of 250-290% was obtained. The polymer prepared in the presence of Z-mercaptoi-ethylthiazole developed, when tested in the same recipe, a tensile strength of 4400-5500 lbs./in. and an elongation of 500- 630%.

In another specific example, '75 parts by weight of butadienewere copolymerized with 25 parts of acrylonitrile at 30 C., while being agitated in the presence of about 250 parts of a 3% solution of myristic acid which had been 85% neutralized with sodium hydroxide, and 0.35 part v of hydrogen peroxide as an initiator. In subsequent polymerizations, 0.4 partof various 2-thiothiazyl compounds were included in the emulsion during the polymerization. The solubilities of the polymers are given in the following table:

Modifier Percent Solubility in benzene azomethane disulfonate.

The polymers formed in the presence of the 2- thiothiazyl compounds were more coherent than the unmodified polymers, were more easily worked on a mill, and exhibited higher tensile strengths and elongations when tested in tire tread recipe. Similar results are obtained when the modifiers of this invention are employed in the emulsion polymerization of other monomeric systems such as mixtures of butadiene and methyl methacrylate.

The proportion in which the modifier is included in the composition depends somewhat upon the properties desired in the product, the higher proportions of modifier in general producing softer, more soluble polymers. Very small amounts of modifier such as 0.1% or even less based on the monomers'in the emulsion may profoundly aifect the nature of the polymer produced, and amounts up to 5% or over may advantageously be employed.

Although the exact manner in which the moditiers of this invention function is not understood, it is believed from the nature of the changes in properties effected by polymerizing monomers in the presence of modifying agents that these materials in some way inhibit the formation of cross-linkages but still permit the formation of long, straight chains of polymerizable monomers.

' It is believed that in the absence of some agent which serves to prevent or inhibit cross-linkage, the products of emulsion polymerizations which have been carried to completion contain numerous cross-linkages which affect the properties of the polymer in much the same manner as the cross-linkages formed during the vulcanization of natural crude rubber with the aid of sulfur change the properties ofthe crude rubber. This theory explains why the polymers prepared in the presence of modifying agents are in general more plastic and more soluble than unmodified polymers.- 'This theory is presented only by way of explanation and is not intended as a limitation on the invention, for regardless of the correctness of the theory, the inclusion in emulsion polymerization batches of a compound containing a 2-thiothiazyl group produces the beneficial results heretofore described.

The modifying agents of this invention may be employed in the polymerization in aqueous emulsion of butadiene hydrocarbons such as butadiene, 2,3-dimethylbutadiene, isoprene, of piperylene either alone or in admixture with each other or with other monomers copolymerizable therewith. As examples of monomers copolymerizable with butadiene may be mentioned such, compounds 'as styrene, vinyl naphthalene, acrylonitrile, methaerylonitrile, methyl methacrylate, vinyl acetate, vinylidene chloride, methyl vinyl ketone, methyl vinyl ether, and similar. unsatu-- such as persuli'ates, perborates, percarbonates.

and the like, as well as other types of initiators such as diazoaminobenzene, and dipotassium di- Any of the ordinarylemulsii'ying agents such as fatty acid soaps including sodium oleate and sodium stearate, hymolal sulfates and aryl suli'onates including sodium lauryl sulfate and sodium isopropyl naphthalene sulfonate. and salts of organic bases containing long carbon chains such as the hydrochloride of dlmethylaminoethyloleylamide, trimethylcetylammonium methyl sulfate, etc., may be employed in the polymerilimit the invention solely thereto, for it will be obvious to those skilled in the art that many variations and modifications are within the spirit and scope of the invention as defined in the-appended claims.

I claim: 1. A method which comprises polymerizing a butadiene hydrocarbon in the form of an aqueous emulsion in the presence or a compound containing the 2-thiothiazyl group.

2. The method which comprises polymerizing in the form of an aqueous emulsion a mixture of butadiene and a monomer copolymerizable therewith in aqueous emulsion in the presence of a compound containing the z-thiothiazyl group.

3. The method which comprises copolymerizing in the form of an aqueous emulsion butadiene and a smaller amount of a monomer copolymerizable therewith in aqueous emulsion, in the presence of an aliphatic 2-mercaptothiazole.

4. The method which comprises copolymerizing butadiene and acrylonitrlle in the form of an aqueous emulsion in the presence of an aliphatic I so 2-mercaptothiazo1e.

5. The method which comprises copolymerizing in the form of an aqueous emulsion butadiene and a smaller amount of a monomer copolymerizable therewith in aqueous emulsion, in the presence of 2-mercapto-4,5-dimethylthiazole.

ing in the. form of an aqueom emulsion butademand a smaller amount of a monomer copolymerizable therewith in aqueous emulsion, in

the presence of an aliphatic bis-thiazyl-2-sulfide.

8. The method which comprises copolymerizing butadiene and acrylonitrile in the presence of an aliphatic bis-thiazyl-z-disulfide.

9. A composition of matter prepared by the method of claim 1.

10. A composition of matter prepared by the method of claim 2.

11. A composition or matter prepared by the method of claim 3.

12. A compodtion of matter prepared by the method of claim 4.

13. A composition of matter prepared by the method of claim '1.

14. A composition or matter prepared the method of claim 8.

CHAR-LB 1'. FRYLING.

Certificate of Correction Patent No.- 2,380,426. i r July 31, 1945.

CHARLES F. FRYLING It is hereby certified that errors appear in the printed specification of the above numbered atent requn'm correction as follows: Page 2, second colulirm, lines 5 and 6,

I for dimet ylaminoethylo eylamide read diethylaminoethyloleylamide; line 23, claim 1,

for A method read The method; and that the 'said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Oflice. J I Y Signed and sealed this 9th day of July, A. D. 1946.

LESLIE FRAZER, r

First Assistant Commissioner of Patents. v 

